We propose and analyze a new class of multichannel optical waveguide junctions. These junctions consist of a multimode channel waveguide that branches into several single‐mode channels. We show that such waveguide junctions, when properly designed, can route each of the spatial modes of the multimode waveguide into a different single‐mode channel. These waveguide junctions should be useful in selective mode excitation, routing, switching, modulation, and wavelength multiplexing/demultiplexing of guided waves, as well as for mode control in semiconductor lasers.